This disclosure relates generally to optical communications, and in particular but not exclusively, relates to a dither technique for locking to a transmission peak in tunable lasers.
Tunable external cavity lasers (ECLs) are widely used in lightwave test-and-measurement equipment and are becoming recognized as essential components for the rapidly expanding field of wavelength division multiplexed (xe2x80x9cWDMxe2x80x9d) optical communication. Tunable ECLs have been developed to provide external cavity tuning of the central lasing wavelength. This external cavity tuning has been achieved using various mechanisms such as mechanically tuned optical gratings used in transmission and reflection. Tunable ECLs must be capable of providing a stable, single mode output at selectable wavelengths while effectively suppress lasing associated with external cavity modes that are within the gain bandwidth of the cavity.
In dense wavelength division multiplexing (DWDM) fiber optic systems, multiple separate data streams propagate concurrently in a single optical fiber, with each data stream created by the modulated output of an ECL at a specific channel wavelength. Presently, channel separations of approximately 0.4 nanometers in wavelength or about 50 GHz are achievable, which allows up to 128 channels to be carried by a single fiber within the bandwidth range of currently available fibers and ECLs. Greater bandwidth requirements will likely result in smaller channel separation in the future. Thus, accurate control over the central lasing wavelength of the ECL is currently desirable and of increasing importance as channel separations decrease.